Stereoselective synthesis of the beta-anomer of 4'-thionucleosides based on electrophilic glycosidation to 4-thiofuranoid glycals

Three types of 4-thiofuranoid glycal with different 3,5-O-silyl protecting groups were prepared and their electrophilic glycosidation was investigated. The 3,5-bis-O-(tert-butyldimethylsilyl)-4-thiofuranoid glycal (5) was obtained through mesylation of 2-deoxy-4-thio-D-erythro-pentofuranose (4) and subsequent base-promoted elimination, while thermal elimination of sulfoxide derivatives was suitable for the preparation of 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) (9) and 3,5-O-(di-tert-butylsilylene) (11) 4-thioglycals. The glycosidation reactions of these 4-thioglycals were carried out, in the presence of either PhSeCl or NIS, by using silylated derivatives of uracil, thymine, cytosine, and N(6)-benzoyladenine. Among the three 4-thioglycals, 11 was found to be an excellent glycosyl donor, forming the desired beta-anomer exclusively irrespective of the nucleobase employed.     

Theory of the shape relaxation of a rouse chain

An analytical interpretation is made for the Monte Carlo results on the shape of an unrestricted random flight chain. Both the average shape and the time correlation function of the shape fluctuation are discussed. The Monte Carlo results are well reproduced by assuming that the shape of the chain is primarily determined by the first few normal modes.     

Studies on the syntheses of heterocyclic compounds. Part DLIV. A total synthesis of (±)-coreximine by thermolysis

Thermolysis of the dibenzyloxy-substituted benzocyclobutene IXc effected cyclization and mono-O-debenzylation to provide a facile route to the total synthesis of the protoberberine isoquinoline (±)-coreximine (XIII).     

General features of photoinduced spin dynamics in ferromagnetic and ferrimagnetic compounds

Ultrafast photoinduced spin dynamics has been investigated by time-resolved magneto-optical Kerr spectroscopy for various ferromagnetic and ferrimagnetic compounds: FeCr2S4, CoCr2S4, CuCr2Se4, CdCr2Se4, La0.6Sr0.4MnO3, and SrRuO3. The temporal demagnetization process, which is observed commonly for all the compounds, essentially consists of two components: One is an instantaneous change which originates perhaps from multiple emissions of magnetic excitations during nonradiative decay of photoexcited carriers, and the other is a delayed response due to thermalization of the spin system. The time constant of the delayed change depends strongly on materials and is scaled with the magnetocrystalline anisotropy, indicating that spin-orbit coupling is a dominant interaction for this process.     

Nonlinear magneto-optical kerr rotation of an oxide superlattice with artificially broken symmetry

Simultaneously broken time-reversal and spatial-inversion symmetries can be realized in the epitaxially grown oxide "tricolor" superlattices composed of three sequential kinds of perovskite layers including a ferromagnetic one (manganese oxide). As a generic feature of such a system, the magnetic-field-induced second-harmonic generation and the resultant Kerr rotation of second-harmonic light were demonstrated. The signal intensity probes the interface magnetization of the superlattice, where temperature variation is shown to be distinct from the bulk feature.     

Enantioselective synthesis of (−)-velbanamine and (+)-isovelbanamine using L-glutamic acid as chiral template

Enantioselective synthesis of (?)-velbanamine(1) and (+)-isovelbanamine (2) has been accomplished using l-glutamic acid as chiral template.